Lightning struck the Washington Diplomats for a second time tonight.

Just as he had done earlier this season in Washington, Cosmos forward Seninho scored the decisive shootout goal - this one coming in the fifth round - to give the Cosmos a 5-4 win at Giants Stadium in the final North American Soccer League regular season game for both clubs.

The Dips, on the strength of three goals by Alan Green, led, 4-2, with 30 minutes left but could not hang on as the Cosmos overcame the wet going created by an all-day, driving rain and turned a seemingly meaningless game into a dramatic contest for the 34,599 in attendance.

"Shouldn't have lost it," said Dips Coach Gordon Bradley, leaning against his locker, speaking in a monotone. "We should never lose when we're ahead 4-2. And in the shootout, it was the same player who beat us last time."

And, Seninho added later, with the same move that won the previous game.

"But," said Bradley, brightening, "this should help our confidence going to Los Angeles."

The Dips will fly to Los Angeles Monday morning to begin a two-game playoff series Wednesday night at 10:30 in Pasadena's Rose Bowl. The return match is set for RFK Stadium at 2:30 p.m. Sunday.

Tonight's loss left the Dips at 19-11, good for 172 points. That means, should they beat Los Angeles, their second-round opponent probably will be the Cosmos. The Cosmos finished 24-6 for 216 points and the best record in the league.

For a long while tonight, it looked like the Dips would send the crowd of 34,599, which turned up despite a driving rainstorm, home disappointed.

It took a tying goal at 85:12 on a rolling shot by Marinho to send the game into overtime at 4-4 and it was Washington that had the best opportunities in the overtime.

The shootout was a near-replay of the Cosmos 3-2 shootout win in Washington.

It was Seninho again who socred to make the difference.With the score 2-2, Sakib Viteskio beat goalie David Breie, only to fire wide right.

Then Seninho, using the same move he had made in Washington, drew out Dip keeper Bill Irwin, slid the ball past on the goalie's left and popped it into the empty net.

"I should have known he was going to do that," said Irwin, shivering in the cold. "But I wasn't sure he'd try it again.

"Unfortunately, he did."

Disappointed by the loss, the Dips insisted it did not overshadow how close they came to winning on the Cosmos' home ground with four starters - Jim Steele, Don Droege, Bobby Stokes, out with suspensions and Bob Iarusci out with flu - on the sidelines. The Cosmos played without leading scorer Giorgio Chinaglia (groin pull) and rested midfielder Ricky Davis.

"We had a lot of players out and they had a couple out," said defender Mike Dillion, who played superbly. "But both teams wanted to win very badly. You play in a rain like that, you play for pride."

Alan Green's three goals gave him a club record 16 for the season. Those and Sonny Askew's eight could not hold off the Cosmos in the last 30 minutes after Washington took a 4-2 lead on back-to-back goals by Green, which came a club-record 64 seconds apart.

"They were just leaving me alone with one defender all night," said Green, in amazement. "I think their defense was very good, to tell the truth. I was open most of the night."

Another Green goal early in the second half was called back by linesman Derrick Smith, who claimed Green was across the 35-yard offsides line when Sakib Viteskic lofted a pass to him.

Video replays showed Green about seven yards onside.

"They played very well in the rain," said the Cosmos' Coach Ray Klivecka, "especially Green. He was near-perfect. Our defense was slow getting back at times. We gave them those two gift goals by Green, and we were lucky to come back."

What Klivecka termed gift goals came with the score 202. Both appeared to be set up by the lake laying the AstroTurf, caused by an all-day, all-night rain.

With the socre 1-1 going into the second half, Askew had faked Santiago Formoso and beat Breic to the goalie's right with an 18-yard shot at 51:21 for a 2-1 Washington lead. The Cosmos tied less than two minutes later on a 12-yard blast by Johan Neeskens.

Then, Green went to work. First he stripped Nelsi Morais of the ball, when the defender slipped, and lofted a 15-yard shot over a surprised Brcic. At 55:58, he took a short pass from Joe Horvath (Horvath's 18th assist, breaking a club record) and popped another 15-yard shot over the 20-year-old goalie.

"Right then we had them," said Bradley. "We had to bunch up on defense, but I think we did it a bit too much."

"The amazing thing about them (the Cosmos) is that they never panic when they're behind," said Gteen. "Nothing fazes them. They just take their time and play their game like they know the goals are going to come. And they do."

The Cosmos' third goal came when Beckenbauer slipped a 20-yard floater past Irwin at 60:07, setting up Marinho's tying goal 25 minutes later.

"We knew we had to just keep pressing," said Beckenbauer. "The goals would come eventually."

For Washington, so did the loss, its fourth straight to the Cosmos since Bradley left as their coach two years ago.

"Can we beat them in the playoff?" Bradley said in answer to a question. "We can, In think. But only if we beat Los Angeles."